Preparation Of Hydroxyapatite Powders And Porous Blocks

Hydroxyapatite is the main inorganic components of bone tissues, has good biocompatibility and biological activity, which is the research hotspot of biological materials. In addition, HAP also has wide application in adsorption, catalysis, fluorescence, semiconductor, cancer areas. The research and development on preparation technology of powder and porous hydroxyapatite is of great importance.In this paper, hydroxyapatite powders and porous hydroxyapatite blocks were synthesised by chemical precipitation and hydrothermal method. With chemical precipitation of hydroxyapatite powders, the affection of solution concentration and solution pH value on the product structure and morphology and agglomeration state were discussed. Experimental results show that CaCl₂ and (NH₄)₂HPO₄ as raw materials, at room temperature, 0.2 mol/L as the initial concentration of the reaction solution, ammonia adjust pH value to 10, aging 24 h under the the laboratory conditions weak crystalline hydroxyapatite powders were prepared; Improving or extending the solution pH, aging time, can improve the conversion rate of hydroxyapatite.HAP powders were prepared by hydrothermal method. With shell powders, diammonium phosphate as raw materials, water treating 3 days at 180℃, shell powders convert into hydroxyapatite directly by the process of"dissolving-recrystallization", crystallinity increased with the hydrothermal reaction time going. As a rich source, having simple making process, low cost, shell powders as raw materials have better economic benefits to prepare the hydroxyapatite.Two different types of salt, calcium chloride and calcium carbonate were used, phosphate as precursor, acetamide for the additive. The results show that intermediate phase has generated among the initial reaction between soluble and insoluble calcium with phosphate, with the hydrothermal reaction time, temperature increasing, eventually transform into HAP. HAP crystal grow along the c axis, forming a large aspect ratio whiskers. Different types of salt as the precursor in hydrothermal formation of hydroxyapatite, the reaction follows a different mechanism, soluble salt follow the"uniform saturated solution precipitation"mechanism, insoluble salt follow the"dissolution- recrystallization"mechanism. Additives acetamide hydrolysis under hydrothermal conditions, forming CH₃COO^-, precisely because of adsorption CH₃COO^- on the HAP crystal surface, thereby reducing the surface energy, effectively avoid the agglomeration of HAP grains, and that the grain grow along the c axis form the whiskers.With calcium carbonate and diammonium phosphate as raw materials, CH₃CONH₂ as additive, porous nest-like HAP material were synthesised by one step hydrothermal method. Its formation mechanism was discussed. The porous material inserted by the HAP whiskers, formed a interconnected porous three-dimensional network structure, with higher porosity. Macropore profit new bone ingrowth; Pore connectivity between each other, favour to the transport of beneficial nutrients and exchange of drug permeability and drug loading capacity of the material. Therefore, this experiment synthetic porous HAP nest material has the potential development value in bone implanted, bone tissue engineering, drug delivery field. The formation of Nest-like porous HAP is due to acetamide hydrolysis to facilitate the slow release of CO₂ gas in system, to achieve the pressure balance system, some the size of the CO₂ bubbles act as the pore-forming role. This method provides a new idea to the preparation of porous materials.